1. Field of the Invention
The present invention relates to a sound receiver having a microphone array.
2. Description of the Related Art
Conventionally, a microphone device having directivity toward a specific speaker direction has been proposed as a sound input device. Such a microphone device is configured, for example, as follows. That is, the microphone device includes, for example, three non-directional microphone units A to C, where a combination of two of these forms a right channel (combination of microphone units A and C) or a left channel (combination of microphone units B and C). In the right channel, a low frequency component in the signal output from the microphone unit A is removed by a high pass filter, a phase of the signal output from the microphone unit C is delayed by a phase shifter, the signal output from the phase shifter is added in reverse phase to the signal output from the high pass filter, and a frequency characteristic is corrected by an equalizer to obtain an output signal. The same process is performed in the left channel so that a configuration enabling sound collection with a high S/N ratio is achieved (for example, refer to Japanese Patent No. 2770593).
Moreover, to achieve a configuration enabling sound collection with a high S/N ratio, a microphone device includes two non-directional microphone units A and B, in which a low frequency component of the signal output from the microphone unit A is removed by a high pass filter, a phase of the signal output from the non-directional microphone unit B is delayed by a phase shifter, the signal output from the phase shifter is added in reverse phase to the output signal of the high pass filter, and a frequency characteristic is corrected by an equalizer to output a signal, (for example, refer to Japanese Patent No. 2770594).
Furthermore, to achieve a configuration enabling miniaturization of the entire structure and to reduce deterioration of the directivity, a microphone device includes two unidirectional microphones, in which an air space of at least 1 cubic centimeter is provided between one of the microphones and an electrical circuit part arranged inside a casing in the maximum sensitivity direction of the one of the microphones, and an air space of at least 1 cubic centimeter is provided between the other one of the microphones and an electrical circuit part arranged inside a casing in a maximum sensitivity direction of the other one of the microphones, (for example, refer to Japanese Patent No. 2883082).
However, when the conventional microphone device described above is set in a place subject to relatively large vibrations, for example, in an interior of a traveling vehicle and the like, in these microphone devices, vibrations in a low frequency band of approximately 0 Hertz (Hz) to 200 Hz, caused by traveling, are received by the microphones. A noise in the signal occurs in the microphones since such vibrations of a low frequency band have a relatively large amplitude that exceeds an amplitude limit point of an amplifier for the microphones. It is known that accordingly, a sound signal corresponding to, for example, sound in a speech frequency band of a person becomes unclear, and there has been a problem in that particularly when such sound is recognized by a sound recognition system, the recognition rate is deteriorated.
In addition, since, for example, improvement of sound collection efficiency from a sound collection direction of the microphone device and phase dispersion are performed, there has been a problem in that such a problem is further aggravated when a microphone device in which a microphone is arranged inside an opening hole of a casing or the like is used because inner walls of the opening hole serve as diaphragms and vibrations generated therefrom reach the microphone as a sound wave.